The present invention relates to an apparatus for processing compacted biomass, such as bales of hay, straw or other similar material, into a form which is suitable to be used to fire a furnace. The material may be fed to the furnace from a chute positioned downstream of the processing apparatus by means of a stoker-type feeding mechanism. The compacted biomass is forwarded in the processing apparatus in a controlled manner by a mainly horizontal conveying system and are opened by cutting the strings or other holding means keeping the bales in a compacted state.
From AU-663,791, on which the preamble of claim 1 is based, it is known to provide an apparatus for processing bales of hay and straw. This apparatus comprises a conveying system of rollers forwarding the bales towards a shredding roller rotated in the same direction but with a relatively high speed compared to the speed of the conveying rollers, and positioned downstream of the conveying rollers. A further roller is positioned downstream of the shredding roller to feed material into the gap between this further roller and the shredding roller, the further roller being rotated in opposite direction compared to the shredding roller, with a lower peripheral speed. The relatively high speed of the shredding roller has a tendency to throw material over and past the further roller in an uncontrolled manner, and the shredding roller has, due to the higher peripheral speed, a tendency to grip more material from the bale than can be transported down between the counter-rotating rollers.
Based on this prior art, it is the object of the present invention to provide an apparatus of this kind which is able to process compacted biomass in an efficient way, reducing the required energy for the processing and yet delivering a processed material sufficiently loosened e.g. to be fed into a furnace by means of a stoker-type feeding system with a screw conveyor or a reciprocating piston.
This is achieved by an apparatus for processing compacted biomass, the apparatus comprising: a conveying system, including controllable drive means, for forwarding compacted biomass in a controlled manner in a mainly horizontal direction; a first rotatable roller and a second rotatable roller positioned downstream of the conveying system, said first and second rollers having their axes of rotation extending generally horizontal and parallel to each other, the first roller being positioned horizontally closer to the conveying system than the second roller so as to first receive the compacted biomass, the first and second rollers being rotated in opposite directions with different peripheral speeds and the rollers being provided with teeth-like elements projecting from the outer surfaces thereof to engage the compacted biomass and passing the biomass through a gap formed between the two rollers, the peripheral speed of the second roller being higher than the peripheral speed of the first roller. The two rollers provide a positive feeding of the material through the gap between the rollers, the first roller controls the speed of feeding into the gap and the faster rotating second roller ensures that all material fed into the gap is quickly removed. The different peripheral speed of the two rollers provides a stretching and thereby loosening of the material with a low energy consumption and with a high reliability. Preferred embodiments are discussed below.